What are teratogens? What factors determine their impact?

What will be an ideal response?

Answer: The term teratogen refers to any environmental agent that causes damage during the prenatal period. The harm done by teratogens is not always simple and straightforward. It depends on the following factors:
• Dose. Larger doses over longer time periods usually have more negative effects.
• Heredity. The genetic makeup of the mother and the developing organism plays an important role. Some individuals are better able than others to withstand harmful environments.
• Other negative influences. The presence of several negative influences at once, such as additional teratogens, poor nutrition, and lack of medical care, can worsen the impact of a single harmful agent.
• Age. The effects of teratogens vary with the age of the organism at the time of exposure. Some parts of the body, such as the brain and eye, have long sensitive periods that extend throughout prenatal development. Other sensitive periods are much shorter. In the germinal period, before implantation, teratogens rarely have any impact. If they do, the tiny mass of cells is usually so damaged that it dies. The embryonic period is the time when serious defects are most likely to occur because the foundations for all body parts are being laid down. During the fetal period, teratogenic damage is usually minor. However, organs such as the brain, ears, eyes, teeth, and genitals can still be strongly affected.